Objectives - Post-stroke depression can be treated with serotonin inhibitors suggesting a role for the serotonin system in these transport patients. The number of platelet serotonin transporters in stroke patients and in control subjects have been measured in this study. Materials and methods - Newly admitted stroke patients who did develop or who did not develop a post-stroke depression, non-acute patients who previously had had a stroke and control subjects were compared. The number of platelet serotonin transporters was analysed by ligand binding methodology. Results - The number of platelet serotonin transporters was low shortly after a stroke compared with normal subjects; no difference was found between the stroke patients who developed a post-stroke depression and those who did not. Conclusion - A low number of platelet serotonin transporters may be a non-specific state marker for a condition as acute stroke.